Embodiments described herein generally relate to imaging systems, particularly to multi-modality imaging systems, such as positron emission tomography (PET)/computed tomography (CT) systems.
CT imaging systems typically include an x-ray source and a detector. In operation, the x-ray source and the detector are rotated around the object to be imaged such that an angle at which an x-ray beam intersects the object changes. A group of x-ray attenuation measurements, or projection data, from a detector at one gantry angle may be referred to as a “view.” A set of views made at different gantry angles during one revolution of the x-ray source and detector may be referred to as a “scan.” In an axial scan, projection data is processed to construct an image that corresponds to a two-dimensional cross-section or slice of an object being scanned.
PET imaging systems may scan objects to acquire image information using non-moving detectors. During operation of a PET imaging system, for example, a patient is initially injected with a radiopharmaceutical that emits positrons as the radiopharmaceutical decays. The emitted positrons travel a relatively short distance before the positrons encounter an electron, at which point an annihilation event occurs whereby the electron and positron are annihilated and converted into two gamma photons that are detected using scintillators, arranged in a ring within an annular gantry. Signals from the scintillators are then processed to produce an image.
It can be beneficial to utilize both CT and PET systems to scan a subject such as in known dual-modality imaging systems. Separate gantries are used in these dual-modality imaging systems. However, having two imaging detector gantries (in tandem) increases the footprint of the system and consequently a larger imaging room is needed. Further, newer CT detectors have an increasingly higher field of view, which increase the CT detector size. The larger CT detector in these dual-modality CT/PET systems results in the PET detector being displaced further along into the bore volume. Thus, the patient travels further into the bore volume, which can cause claustrophobia and general discomfort for certain patients. In addition, as a result of the increased travel length, the patient table has to be made stronger with additional reinforcements.
Some known dual-modality imaging systems attempt to reduce the distance between detectors of the different modalities. For example, some systems co-locate the PET detectors and the CT detectors on a common rotating portion of the gantry. However, it is not always desirable to rotate the PET ring. Other systems position the CT and PET detectors side by side and provide a moving patient platform. However, this arrangement increases the difficulty of co-registration and alignment.